Electrode for electrical discharge devices



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P 1943- G. E. lNMAN 2,329,118

ELECTRODE FOR ELECTRICAL DISCHARGE DEVICES Filed July 12, 1941 FigZ.

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lnve ntor e01 e Elnman, I b9 His Accorneeg.

Patented Sept. 7, 1943 4 ELECTRODE roe ELECTRICAL DISCHARGE DEVICES George Inman, East Cleveland, Ohio, assignor to General Electric Companfla corporation of New York Application July 12, 1941QSerijalNo. 402,117

('ci.1-25o'-"27.5)

9 Claims.

This invention. relates to electrodes for electrical discharge devices, and particularly to cathode construction for such devices. The invention is very' advantageous for fluorescent electric lamps .or' tubes, and is hereinafter explained with special reference to its use in such lamps. The requirements for-cathodes of fluorescent tubes are somewhat contradictory; and difficulty has been experiencedin reconciling thecontradictions in one construction. On the -onehand, it 'is'desirable that the cathode should heat'up and become fully, emissivevery quickly,ywhi ch hassuggested a construction consisting of fine refractory metal wire compactly coiled, and coated or impregnated with refractory electronemiss'ivematerial. On the other hand, it is de sirable that the active cathode surfaceshould allbe at substantially the same potentiaLwhich would require a moremassive cathode structure to airord-highconductivity. "If, moreover, the

' cathode-is very thing-as in'a coil of fine wire,

the spot; wherelthe electric discharge or are strikes may become locally'overheated, and may even get so hot that emissive materialon'the cathode coil vaporizes and deposits on the nearby wall of the lamp tube. 7 I

One construction that hasbeen proposed conjsists of acoiled coilof fine wire with the mandrel wireon which the first and smaller coil is wound left inplace in this small coiLwhenahdafter the latter is wound into a larger coil, to serve I as a current conductorin the completed -tube I or lamp. This, however, has proved to be sub ject to the drawbacks of; not heating up quickly enough; furthermore, it'isidiificult to get a sumcient amount of activating material to adhere to such a cathode, or-to remain in intimate contact ith themetal, i I 7 In accordance with my invention, I meetand reconcile the contradictory cathode requirements aboveindicateiand overcome the drawbacks of prior constructions, by a peculiar structural combination: For the-m0re' active portion of the cathodeffI employ; a coil of tungsten or other metal wire (whether round, or of angular or flattened cross-'seotiom like a strip or ribbon) which may be 'of a size suitable for rapid heating and easy starting. Withthis I associate a conductor wire or'rod which is larger in cross section, and engages the convolutions or turns of the finer wire at a series'of isolated points. The conductor wire maybe fitted to the coil so that they inter-engage at points corresponding to their cross-sectional configurationsgwhich are here shown as dis'sim'ilar,one round and the other polygonal, orsubstantially so. This conductor wire may be considerably larger than the fine wire, so as to carry current easily to the sections of the convolution of the fine wire, and to receive heat from sections that tend to overheat andredistribute it to other sections and convolutions -thus equalizing-and keeping down the temperature of the active portion of; the

cathode sufiiciently to prevent objectionable heat effectson theemissive material of thecathode. fI'he'structure :is' relatively strongand rugged, yet therejis' room and surface for an ample quantity of activating material, both on the fine'wire and in contact with the base or conductor wire.

One form'that such a" construction may take consists of around helical coil of finer wire with a polygonal conductor wire. therein engaging each convolution of the -aforementioned coil at the angles or vertices of th'e polygonalcross section. For example, the largerwire may be triangularfand preferably equilateral; or quadrangular, and preferably" square; or even-pen-- tagonal; hexagonal, etc. Another form of construction consists of a polygonal "coil off finer" wire with Ia circular or polygonal conductor wire therein engaging'eachconvolution of the fine wire'at a 'series' of points each "of which] is intermediate in the lengthier a side of the polygon 'formedb'y the convolution. 1

When the conductor" wi re is'i 'circular, the sides of each polygonal convolution of the other wire are tangent to the peripheryof'theconductor wire." .1 In any of the' form's above mentioned'or indicated, the'coil of finer wire and the J conductor wire engaged thereidm'ajy themselves be coiled up into a larger coil, and this recoiling' may be repeated if desired.- Isolated points of'engage- I mentof the finer wire with each convolution of the other wire maybe fixed and maintained by the mere configuration of the conductor wire and the coil of fine wire, without welding at the points of contact; or the'wires maybe welded where they engagefif this is thought desirable for reae sons [of better electrical or'thermal conduction, or greater mechanical stifiness, or for any other .rea son v '1 Other features and advantagesof the invention will becomeapparent-from the following description of species and forms of embodiment,

and from the drawing.

In the drawingliig. l'is a general side View of a coiled coil'cathodeconstruction conveniently e bodying theinvention; and Fig. 2 i s a frag-- mentary side view'onalarger scalej Fig. 3 shows a cross-section of one preferred form of cathode construction embodying the invention, on a still larger scale than Fig. 2; Fig. 4 is a corresponding fragmentary side view, before the second coiling; and Figs. 5 and 6 are similarviews illustrating a modification of the form shown in Figs. 3 and 4.

Figs. 'land 8 are views similar to, Figs. 2-6 illustrating another preferred fonn of cathode I construction; and Figs. 9 and 10 are similar views illustrating a modification of the form shown in Figs. '7 and 8. h

Figs. 11, 12, l3, l4 and are cross-sectional views similar to Figs. 3 and 5, illustrating other forms of cross-section of the conductor wire with the associated coil of other wire, Fig. 11 showing a polygonal conductor wire with convexly rounded sides, Figs. 12 and 13 showing polygonal concathode; while the particular point where the arc strikes can be as hot as is desirable without overheating objectionably.

1 For both the form of construction illustrated inFigs. 3-6 and that illustrated in Figs. 7-10, considerable flexibility of design is possible, not only by varying the pitch of the coil of wire II or He, and the relative sizes of the wires II or I Ia and I5 or I511, but also by varying the number of points of contact between each convolution of the wire II or Ha and the wire. I5 or, I5q,;and the consequent degree of proximity of the wire it or Ila to the wire I 5 or I5a bjetweezrthe points oi contact. A further factor of flexibility. in design is the choice between polygonal and circular wires I5 and lie, giving eitherha more or less normal type of contact as in Figs. 3-6, or

' a tangential contact as in Figs. 7-10, and the than the wire 11,81 150 connected to the lead wire supports I2, I2. As shown in Figs. 3'6 the wire is formed intoa roundcoil, preferably circu lanwhile the wire I5 is of polygonal cross-sect on. which mayb n lerflwdeq ilat l in Figs. 3 and 4, or quadrangular and square, as in "Figs. '5 and'fi. The wire .II may receive its first coiling by winding it directly on the polygonal wire IE-as a mandrehunder such relatively light tension thatthe coil of, wire II does not confirm to t eansu r 9 e w e ..-.bi1t remains of a rounded or-circular configuration or the wire II may first be Wound on a round mm. and. s p ed; o er ew se s p e J In .either case, the wire I5 with the coil of wire II there nmay afterward be coiled on;.a mandrel n show bu pr ie b ril rse n the W r i): to make the coiled oi ho ni ig an 1 As shown in Figs.;7-10;thecoi l of wire .IIia-is of; polygonal c ross-, s ecti on, which may ;be triangular and equilateral, as in Figs. 77 and 8, or quadrangular and square, as .in Figs. 9 and 10. In either case, the wire coil I'Ia 'is first wound ne nol so a mand e m h wn and t a removed and. slippedover the round gwire {5a.

After-this, the wire ISQ, with thecoil-I Ia thereon is coiledon ,another mandrel- (not -sh owni to make thecoiledicoi how n FiES-I mu-v In all the. forms-of construction illustrated and described, practically the. entire surface of the .wire H or IIa that forms the more active portion of the cathode is available and sufficiently exposed for coating with activating electronemissivema er ahe u h s r uskwe lw 1 refractory oxides which may also come in contact with the base or conductor-wire I5 or I at thepoints of engagement between the two wires,

oreven coat the wire I5 or I5a completely. More ever, the spacing of the-wire I Ior I Ia;from the wire I5 or I50. provides space for the activating material and recesses favorable to its retention. Theconductor wire I5 or I541 engageseach convolution or turn of the coiled wire I I or I In at a series of fixed isolated-points;which -provide conductor wire.

form. cross-section, Figs. 14 and 15. By lateral hollowing of the conductor wire I5 along-tits length, increased space for activating materialis aflorded'because the coil convolutions II '(into the wire .I ifits) lie further away from the re-entrant conductor surface with which they are out of contact. Or the 'wire I5 or 1.5a for the forms on construction represented in Figs, 3-10 might be larger than thereshown in relation to the} size of the coil II er Illa, so that the coil .convolutions wouldhave to be bent outward at their points of contact withthewire I5 05 I5a, l figs.i6 and17.-', --Wh at Iclaim as'new-and desire to secure by Letters Patent of the United States is: V 1 H A cathodecomprising as its'membersawire coil forming-an. active'portion of the cathode, and a conductor wire larger than the coiled wire extending through the coil and fitted directly to said coihone of .the said members having a polygonal configuration, sothat the conductor wire engages the coil convolutions only at isothe-active portion of the cathode and a larger polygonal conductor wire extending-therethrough and engaged with the convolutions of the said coil only at a series of isolated points corresponding to angles of the polygonal cross-sectionofthe h 3. A cathode as setforth-in claim 2 wherein the conductor wire is substantially triangular.

4. A cathodeas set forth in claim/2 wherein the conductor wire is substantiallyquadrangular. -5. A cathode comprising a polygonal coiiof Wire forming the active portion of the cathode, e

and a larger conductor wire extending therethrough and engaged with the convolutions of the said polygonal coil onlyat a series of isolated points, each intermediate in the length of a side 10 the convolutions.

' ,8. A cathode as set forth in claim 1 wherein the cross-section of the conductor Wire is a hollow-sided figure.-

9. A cathode comprising a coil of wire forming the active portion of the'cathode, and a larger conductor wire of difierent cross-sectional configuration from said coil extending therethrough and fitted directly thereto, but laterally hollowed along its length and largely out of contact with GEORGE ElINMAN 

